Ertapenem of formula (1) has chemical name (4R,5R,6S)-3-[(3S,5S)-5-[(3-carboxyphenyl)amino]formyl]-pyrrolidine-3-yl]thio-6-[(1R)-1-hydroxyethy]-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate, which is a new carbapenem antibiotic joint developed by Merck and Astrazeneca, and has good antibacterial activity against gram-positive bacteria and gram-negative bacterium.

Ertapenem is obtained by deprotection of the intermediate of Ertapenem of formula (2).
Np represents
P1 and P2 represent carboxyl protecting groups; and P3 represents carboxyl protecting groups, H or Na.
Compound 2 is typically prepared by condensing the carbapenem parent nucleus 3 with the side chain of Ertapenem 4 in the presence of base. The synthesis route is shown in Scheme 1:

U.S. Pat. No. 5,478,820A discloses compound 2, wherein P1, P2 and P3 are all allyl, or compound 2 wherein P1 and P2 are p-nitrobenzyl (referred to as PNB hereinafter) and P3 is allyl, and their preparation methods.
U.S. Pat. No. 6,504,027 B1 provides a one-pot-process for producing Ertapenem sodium, which comprises condensing the carbapenem parent nucleus 3 (P1 is PNB) with the side chain of Ertapenem 4 (Np is
and P3 is H) and deprotection by hydrogenolysis. WO 02/057266 and WO 03/026572 reported similar processes.
WO 98/02439 provides a process for producing compound 2 wherein P1 and P2 are both PNB and P3 is H, which comprises condensing the carbapenem parent nucleus 3 (P1 is PNB) with the side chain of Ertapenem 4 (P2 is PNB, and P3 is H) in the presence of base such as diisopropylamine with a conversion rate greater than 98%. But the aftertreatment and products obtained were not reported therein.
WO 2008/062279 provides a process for producing compound 2 wherein P1 and P2 are both PNB and P3 is H or Na+. For the aftertreatment of compound 2 with P3 being H, the reaction mixture was poured into buffer solution (pH=7) or water, or a mixture of buffer solution (pH=7) (or water) with ethyl acetate, and compound 2 was obtained after subsequent treatment. For the former situation, it is readily to bring about adhesion of the product and result in difficulties in aftertreatment and a poor purity (below 90%) of the product; for the latter situation, the product can not be obtained in form of solid and the process went against environmental protection due to the use of organic solvent. This application doesn't provide the physicochemical properties of the product, nor perform structure identification of the product. This application also reports a process for producing compound 2 with P3 being Na+ and amorphous form thereof. The introduction of sodium source results in increase of total amount of inorganic salts in subsequent reactions and thus the aftertreatment is not readily to be performed, which goes against the crystallization of product.
Consequently, there is no report on the physicochemical properties of compound 2 with P3 being H in prior art, and compound 2 with P3 being H can not be obtained in a high purity by the prior art. In other words, using the prior art, compound 2 with P3 being H can not be obtained thereby structure identification and physicochemical properties measurement can be performed.